Potassium hydride dimer

Another factor to consider is the energy required to break solid MH into individual molecules. Calculate the dissociation energies for sodium hydride dimer and potassium hydride dimer, i.e. 

ET-IR spectroscopy was employed to investigate the structures of the 1 1 complexes between Li" and the guanidine-substituted azo compounds pyiidine-2-azo-p-phenyltetramethylguanidine and 4,4 -bis(tetramethylguanidine)azoben-zene. Both Li" complexes exist as dimers in acetonitrile solution.The structural chemistry of potassium N,N -di(tolyl)formamidinate complexes has been investigated in detail. These compounds were prepared by deprotonation of the parent Af,N -di(tolyl)formamidines with potassium hydride (Scheme 13). The resulting adducts with either THE or DME display one-dimensional polymeric solid-state structures that exhibit /r-fj fj -coordinated formamidinates. 

Electron-rich olefins are nucleophilic and therefore subject to thermal cleavage by various electrophilic transition metal complexes. As the formation of tetraaminoethylenes, i.e., enetetramines, is possible by different methods, various precursors to imidazolidin-2-ylidene complexes are readily available. " Dimerization of nonstable NHCs such as imidazolidin-2-ylidenes is one of the routes used to obtain these electron-rich olefins [Eq. (29)]. The existence of an equilibrium between free NHC monomers and the olefinic dimer was proven only recently for benzimidazolin-2-ylidenes. In addition to the previously mentioned methods it is possible to deprotonate imidazolidinium salts with Grignard reagents in order to prepare tetraaminoethylenes. " The isolation of stable imidazolidin-2-ylidenes was achieved by deprotonation of the imidazolidinium salt with potassium hydride in THF. ... 

The preparations of lithium and sodium (cyclooctane-1,5-diyl)dihydro-borates(l-) in tetrahydrofuran proceed via isolable, stable etherates. These can be made solvent-free simply by heating under vacuum. 9-Borabicyclo[3.3.1 ]-nonane dimer (9-BBN) can easily be prepared from cycloocta-1,5-diene2 by reaction with tetraethyldiborane(6), tetrahydrofuran-borane8,9 or dimethyl sulfide-borane.10 The synthesis of alkali metal (cyclooctane-1,5-diyl)dihydroborates is achieved by addition of 9-BBN to a suspension of the alkali metal hydride in tetrahydrofuran. Lithium hydride reacts more slowly than sodium or potassium hydride. The reactions are brought to completion by heating under reflux. 

It is important to consider interactions between NHCs and alkali metals since, in many cases, NHCs are generated by deprotonation of a precursor molecule using an alkali salt of a strong base, such as potassium teri-butoxide, sodium hydride, potassium hydride, or u-butyllithium [19,20]. The influence of alkali metals in solution on stable diaminocarbenes has been investigated by C NMR and it has been postulated that metal ions in solution may act as catalysts for the dimerization of these NHCs [21]. Crystallographically characterized group 1 centers with coordinated neutral NHC ligands, however, are few and far between. 

Arduengo et al. obtained the first stable thiazol-2-ylidene 104 by deprotonation of the corresponding thiazolium salt 103 with potassium hydride in THF (Scheme 1.14). In the presence of protons, NHC 104 dimerized to olefin 104=104 and an equilibrium between monomer and dimer was observed. Both 104 and 104=104 were the first and only carbene/olefin pair where both components could be characterized crystallographically. Thiazol-2-ylidenes with sterically less demanding A-substituents like mesityl or methyl, however, dimerized rapidly at room temperature and only their dimers can be iso-lated. None of the analogous benzothiazol-2-ylidenes could be isolated up to now, although benzothiazolium salts 105 and complexes of benzothiazol-2-ylidenes are readily accessible. ... 

Arduengo et al. obtained the first stable thiazol-2-ylidene 119 by deprotonation of the thiazolium salt 118 with potassium hydride in THF (Scheme 1 14) 188 presence of protons, NHC 119 dimerized to yield olefin... 

Reinhoudt, Gray, Smit and Veenstra prepared a number of monomer and dimer crowns based on a variety of substituted xylylene units. They first conducted the reaction of 1,2-dibromomethylbenzene and a polyethylene glycol with sodium hydride or potassium Z-butoxide in toluene solution. Mixtures of the 1 1 and 2 2 (monomer and dimer) products were isolated and some polymer was formed . The reaction was conducted at temperatures from 30—60° and appeared to be complete in a maximum of one hour. The authors noted that the highest yield of 1 1 cyclic product was obtained with disodium tetraethylene glycolate instead of dipotassium hexaethylene gly-colate (see also Chap. 2) . Chloromethylation of 1,3-benzodioxole followed by reaction with disodium tetraethylene glycolate afforded the macrocycle (29% yield) illustrated in Eq. (3.20). 

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